1. Field of the Invention
This invention relates to a DC--DC converter, and more particularly to a DC--DC converter based on a forward type which can be built as a compact one with low price.
2. Description of the Prior Art
FIG. 5 shows the DC--DC converter disclosed in Japanese Patent Laid-Open Publication No. HEI2-65659.
In this DC--DC converter 51, current flow to the coil L by turning ON the transistor Tr, and energy is accumulated in the coil L from the DC power supply Eb. Then, when the transistor Tr is turned OFF, resonance is generated by the coil L and the resonant capacitor C. If voltage in the coil L is in the reverse direction to that in the DC power supply Eb, energy accumulated in the coil L flows to the smoothing capacitor CF as DC output and furthermore is supplied to the load RL.
The DC output can be stabilized by adjusting the transistor Tr ON period and setting the ON/OFF cycle constant.
On the other hand, when the switch S is turned ON during the time that the transistor Tr is ON, current due to energy accumulated in the coil L flows through the diode D, so that resonance is stopped.
The conventional DC--DC converter 51 described above is based on a flyback type, which causes many problems. For instance, a peak value of the charging current flowing via the rectifier DD to the smoothing capacitor CF becomes larger and the coil L, rectifier DD and smoothing capacitor CF must all be usable for large current.
Also, since energy of about 2 times larger than the output energy must be accumulated in the coil L during the transistor Tr ON period, the size of the coil L becomes large.
Also, as a peak value of the current is large, much noise is generated.
Thus, the object of this invention is to provide a DC--DC converter, in which components such as a coil, a rectifier and so on for small current are available and which can be minimized in size and in which noise is not generated much.